The present invention relates to a cold cathode field emission device, a cold cathode field emission display and processes for the production thereof. More specifically, it relates to a cold cathode field emission device having the form of a column, a flat panel type cold cathode field emission display having a plurality of the cold cathode field emission devices arranged in a two-dimensional matrix, and processes for the production thereof.
Studies are being made on various flat panel type displays for an image displaying unit which is to replace currently main-stream cathode ray tubes (CRT). The flat type displays include a liquid crystal display (LCD), an electroluminescence display (ELD) and a plasma display (PDP). Further, there is also proposed a cold cathode field emission display from the viewpoint of a brightness on displaying.
The above cold cathode field emission display (to be sometimes simply referred to as "field emission display" hereinafter) has a plurality of pixels as its conceptual view and is shown in FIG. 33, and each pixel comprises a plurality of Spindt type cold cathode field emission devices (to be sometimes simply referred to as "Spindt type field emission device" hereinafter) arranged in a two-dimensional matrix form. Each Spindt type field emission device comprises a patterned electrode layer (cathode electrode layer) 11, an insulating interlayer 12, a gate electrode 14 formed on the insulating interlayer 12 and an emitter electrode 102 formed in an opening portion formed in the insulating interlayer 12.
For example, the cathode electrode layer 11 is formed on a dielectric supporting substrate 10 constituted of a glass substrate, and the cathode electrode layer 11 is composed, for example, of niobium (Nb). The cathode electrode layer 11 and the dielectric supporting substrate 10 are covered with the insulating interlayer 12. The emitter electrode 102 is a conical tip which is formed on the cathode electrode layer 11 according to a semiconductor production process and has a diameter of approximately 1.0 .mu.m. The emitter electrode 102 is composed of molybdenum (Mo) or the like. On the top end side of the emitter electrode 102 is provided the gate electrode 14 so as to surround the emitter electrode 102. A voltage is applied between the emitter electrode 102 and the gate electrode 14 to generate an electric field, and due to the electric field, electrons are extracted from the top end of the emitter electrode 102. The electrons are attracted to a second electrode layer (anode electrode layer) 21 formed on a transparent substrate 20 to collide with a fluorescent layer (light emitting layer) 22 formed between the anode electrode layer 21 and the transparent substrate 20, and as a result, the fluorescent layer 22 emits light, and an intended image can be obtained. The performance of the Spindt type field emission device is controlled in principle on the basis of a voltage to be applied to the gate electrode 14. Such a display is disclosed, for example, in U.S. Pat. No. 4,857,161. The process for the production of the Spindt type field emission device disclosed in the above U.S. Patent will be outlined with reference to FIGS. 34A, 34B, 35A and 35B, hereinafter.
[Step-10]
A niobium layer is formed on a dielectric supporting substrate 10 constituted, for example, of a glass substrate, and then the niobium layer is patterned to form an electrode layer (cathode electrode layer) 11. Then, an insulating interlayer 12, for example, of SiO.sub.2 is formed on the entire surface by a CVD method. Further, a gate electrode 14 is formed, for example, by forming a metal layer on the insulating interlayer 12 by a CVD method and then patterning the metal layer. Then, an opening portion 15 is formed in the gate electrode 14 by lithography and dry etching methods. Further, the insulating interlayer 12 below the opening portion 15 is etched to form an opening portion 13 in the insulating interlayer 12 (see FIG. 34A).
[Step-20]
Then, a peeling-off layer 100 composed of aluminum is formed on the gate electrode 14 by oblique vapor deposition of aluminum (see FIG. 34B). Aluminum is obliquely vapor-deposited such that sputtered particles of aluminum arrive onto the gate electrode 14 with an angle tilted at approximately 75.degree. with regard to the normal of the gate electrode 14. As a result, aluminum is deposited to form the peeling-off layer 100 having "eaves" extending from an edge portion 15A of the opening portion 15 formed in the gate electrode 14. As a result, the opening portion 15 is decreased in diameter by the peeling-off layer 100.
[Step-30]
Then, a metal layer 101 is formed by vertical vapor deposition of molybdenum, whereby an emitter electrode 102 of molybdenum having a conical tip is formed in a bottom portion of the opening portion 13 (see FIG. 35A).
[Step-40]
Then, the peeling-off layer 100 is peeled off from the surface of the gate electrode 14 by an electrochemical process and a wet process, to selectively remove the metal layer 101 on the gate electrode 14 (see FIG. 35B), whereby a Spindt type field mission device having the structure shown in FIG. 33 an be obtained.
In the Spindt type field emission device having the structure shown in FIG. 35B, the electron emitting characteristic thereof is greatly dependent upon a distance from the edge portion 15A of the opening portion 15 formed in the gate electrode 14 to the top end portion of the emitter electrode 102. And, the above distance is greatly dependent upon the process accuracy of the form of the opening portion 15, upon the dimensional accuracy of the diameter of the opening portion 15 and upon the thickness accuracy of the metal layer 101 formed in [Step-30]. It is therefore required to carry out the formation of the metal layer 101 uniformly all over the entire surface of the dielectric supporting substrate for producing the field emission display having a plurality of Spindt type field emission devices having uniform characteristics. Further, if the metal layer 101 cannot be vertically deposited, the distance from the top end portion of the conical emitter electrode 102 to the gate electrode 14 varies among Spindt type field emission devices. As a result, the image displaying characteristics of the field emission display, such as brightness of an image, vary. However, it is very difficult to vertically deposit the metal layer 101 having a uniform thickness all over the entire surface of a large-area dielectric supporting substrate for producing a large-area field emission display, and not only an in-plane variation of thickness of the metal layer 101 on the dielectric supporting substrate but also a variation of thickness among lots are also liable to occur. Moreover, a large-scale deposition apparatus is required. Further, since it is required to deposit the metal layer 101 having a thickness of approximately 1 .mu.m or more by a vapor deposition method, the throughput is low.
Furthermore, it is required to form the peeling-off layer 100 by an oblique vapor deposition method. However, it is difficult to accurately form the above peeling-off layer 100 all over the entire surface of the dielectric supporting substrate having a large area, and it is also difficult to accurately deposit the peeling-off layer 100 such that the peeling-off layer 100 extends from the edge portion 15A of the opening portion 15 formed in the gate electrode 14 so as to have "eaves". Further, the formation of the peeling-off layer 100 varies not only in the in-plane of the dielectric supporting substrate but also among lots.
Furthermore, not only it is very difficult to peel off the peeling-off layer 100 all through the entire surface of the glass substrate having a large area for producing the field emission display having a large area, but also the peeling of the peeling-off layer 100 causes a contamination which results in a decrease in the production yield of the field emission displays.
Moreover, since the height of the conical emitter electrode 102 is defined by the thickness of the metal layer 101 mainly, the freedom of design of the emitter electrode 102 is decreased. Furthermore, since there is a difficulty in determining the height of the emitter electrode 102 as required, the insulating interlayer 12 is inevitably decreased in thickness when the distance from the emitter electrode 102 to the gate electrode 14 is decreased. However, when the insulating interlayer 12 is decreased in thickness, the capacitance between the gate electrode 14 and the cathode electrode layer 11 cannot be decreased, so that the load on the electric circuit of the field emission display increases and further there are caused problems that the in-plane uniformity and the image quality of the field emission display are downgraded.
An emitter electrode having the form of a column is disclosed, for example, in JP-A-9-139173. However, the method of forming the emitter electrode disclosed in the above JP-A-9-139173 is entirely different from the method of forming a cold cathode field emission device or a cold cathode field emission display, provided by the present invention. It is also required to form an insulating layer 7 of SiO.sub.2 by a Chimney vapor deposition method for forming the emitter electrode, while it is difficult to form the insulating layer 7, with a high accuracy, all over the entire surface of a glass substrate having a large area for producing a field emission display having a large area. Further, it is required to remove part of the insulating layer 7 and part of the gate electrode 8 together by a wet method using a peeling liquid. Not only it is very difficult to remove them from the entire surface of the glass substrate having a large area, but also the peeling causes a contamination.